English

Noun

Particulates, alternatively referred to as
particulate matter (PM) or fine particles, are tiny particles of
solid or liquid suspended in a gas. In contrast, aerosol refers to particles and
the gas together. Sources of particulate matter can be man made or
natural. Some particulates occur naturally, originating from
volcanoes, dust storms,
forest and
grassland fires,
living vegetation, and sea spray.
Human activities, such as the burning of fossil fuels
in vehicles, power
plants and various industrial processes also generate
significant amounts of aerosols. Averaged over the globe,
anthropogenic aerosols—those made by human
activities—currently account for about 10 percent of the
total amount of aerosols in our atmosphere. Increased levels of
fine particles in the air are linked to health hazards such as
heart
disease, altered lung function and lung
cancer.

Scale classification

Among the most common categorizations
imposed on particulates are those with respect to size, referred to
as fractions. As particles are often non-spherical (for example,
Asbestos
fibers), there are many definitions of particle
size. The most widely used definition is the aerodynamic
diameter. A particle with an aerodynamic
diameter of 10 micrometers moves in a gas
like a sphere of unit density (1 gram per cubic centimeter) with a
diameter of 10 micrometers. PM diameters
range from less than 10 nanometers to more than 100
micrometers. These
dimensions represent the continuum from a few molecules up to the size where
particles can no longer be carried by a gas.

The notation PM10 is used to describe particles
of 10 micrometers or less and PM2.5 represents particles less than
2.5 micrometers in aerodynamic
diameter. .

But because no sampler is perfect in the sense
that no particle larger than its cutoff diameter passes the inlet,
all reference methods allow a high margin of error. These are also
sometimes referred to with other equivalent numeric values.
Everything below 100 nm, down to the size of individual
molecules is classified as ultrafine
particles (UFP or UP).

Note that PM10-PM2.5 is the difference of PM10
and PM2.5, so that it only includes the coarse fraction of
PM10.

These are the formal definitions. Depending on
the context, alternative definitions may be applied. In some
specialized settings, each fraction may exclude the fractions of
lesser scale, so that PM10 excludes particles in a smaller size
range, e.g. PM2.5, usually reported separately in the same work .
Researchers suggest that even short-term exposure at elevated
concentrations could significantly contribute to heart
disease.

Researchers at the Johns Hopkins Bloomberg School
of Public Health have conducted the largest nationwide study on the
acute health effects of coarse particle pollution. Coarse particles
are airborne pollutants that fall between 2.5 and 10 microns in
diameter. The study, published in the May 14, 2008, edition of
JAMA, found evidence of an association with hospital admissions for
cardiovascular diseases but no evidence of an association with the
number of hospital admissions for respiratory diseases. After
taking into account fine particle levels, the association with
coarse particles remained but was no longer statistically
significant.

The smallest particles, less than 100 nanometers
(nanoparticles),
may be even more damaging to the cardiovascular system. There is
evidence that particles smaller than 100 nanometres can pass
through cell membranes and migrate into other organs, including the
brain. It has been suggested that particulate matter can cause
similar brain damage as that found in Alzheimer
patients. Particles emitted from modern diesel engines (commonly referred
to as Diesel
Particulate Matter, or DPM) are typically in the size range of
100 nanometres (0.1 micrometres). In addition, these soot particles also carry carcinogenic components like
benzopyrenes
adsorbed on their surface. It is becoming increasingly clear that
the legislative limits for engines, which are in terms of emitted
mass, are not a proper measure of the health hazard. One particle
of 10 µm diameter has approximately the same mass as 1 million
particles of 100 nm diameter, but it is clearly much less
hazardous, as it probably never enters the human body - and if it
does, it is quickly removed. Proposals for new regulations exist in
some countries, with suggestions to limit the particle surface area
or the particle number.

The large number of deaths and other health
problems associated with particulate pollution was first
demonstrated in the early 1970s and has been reproduced many times
since. PM pollution is estimated to cause 22,000-52,000 deaths per
year in the United States (from 2000) and 200,000 deaths per year
in Europe.

Regulation

Due to the health effects of particulate matter,
maximum standards have been set by various governments. Many
urban
areas in the U.S. and Europe still frequently violate the
particulate standards, though urban air on these continents has
become cleaner, on average, with respect to particulates over the
last quarter of the 20th century.

EU legislation

Affected areas

The most concentrated particulate matter
pollution tends to be in densely populated metropolitan areas in
developing countries. The primary cause is the burning of fossil
fuels by transportation and industrial sources.

Aerosol science

The field of aerosol
science and technology has grown in response to the need to
understand and control natural and manmade aerosols.